Variability of heart rate, P-R, QRS and Q-T durations in twins.

During a cardiovascular risk factor study, electrocardiograms were done on 355 sets of middle-aged male monozygotic and dizygotic twins. Potential genetic variability in ventricular rate and P-R, QRS, and Q-T duration was investigated using classical statistical twin methodology. Significant genetically determined variability was found for ventricular rate and P-R interval. These findings suggest that heart rate and, to a lesser extent, atrial depolarization are under genetic control with 54% and 34%, respectively, of the variation among individuals explained by heredity.